NAME

XovListClasses − get list of overlay visual classes

SYNOPSIS

#include <X11/XOverlay.h>
XovClassMap ∗XovListClasses(display, return_numbers_of_classes_per_screen)
Display∗display;
int∗∗return_numbers_of_classes_per_screen;
typedef struct _XovClassMap {
inttype;
intvalue;
}  XovClassMap;

ARGUMENTS

display Specifies the connection to the X server. 

return_numbers_of_classes_per_screen
Return value: an array in which each element corresponds to one screen of the display. The element specifies the number of overlay visual classes available for the screen.

DESCRIPTION

The X11 protocol does not support any visual classes corresponding to overlay plane visuals.  The Stardent Overlay extension adds this functionality to the basic protocol.  Two possible class types, OverlayType and StaticOverlayType can be returned by XovListClasses. 

The core X protocol defines these visual class values only: StaticGray, GrayScale, StaticColor, PseudoColor, TrueColor, and DirectColor.  Additional visual class values Stardent might assign to support overlay planes might conflict with other vendors’ protocol extensions.  Thus, a level of indirection is necessary. The Stardent Overlay extension defines the two visual class types local to the extension: OverlayType and StaticOverlayType.  The extension itself returns visual class values that are X server implementation-specific.  It is the visual class value, not the type, which can be used as input to XGetVisualInfo(3X11). 

OverlayType and StaticOverlayType classes are analagous to the PseudoColor and StaticColor visual classes: color maps with a visual class value of OverlayType have writable color table entries; color maps of class StaticOverlayType have read-only entries. 

The return_numbers_of_classes_per_screen variable is a pointer to an array, one element per screen of the display. XovListClasses fills each element of this array with the number of supported overlay visual classes for the corresponding screen. 

The return value of XovListClasses is a pointer to another array, spanning all screens, of the actual overlay visual class values. 

The explicit return value and the indirect return array, return_numbers_of_classes_per_screen, must be freed using XFree(3X11). 

EXAMPLE

Suppose the display has two screens: screen 0 supports two overlay visual classes, and screen 1 supports one overlay visual class. In this case, elements 0 and 1 in the return array will contain the overlay visual class values for screen 0, and element 2 will contain the class value for screen 1. 

SEE ALSO

XovIntro(3X11), XovInitExtension(3X11), XovListInvisiblePixels(3X11), XFree(3X11), XGetVisualInfo(3X11)

FILES

/usr/include/X11/extensions/XovProto.h

March 13, 1992